The present invention relates to a coating for water blocking agents, which is applied in advance, for example, to the joints of sheet piles for constructing a continuous water blocking wall and, after being driven into the ground, absorbs water in the ground and swells and thereby fill empty joint spaces to effect cutoff of water (water blocking), to a sheet pile or steel tubular pipe for water blocking construction methods with the coating applied thereto, and to a water blocking construction method utilizing these.
Continuous walls composed of sheet piles and used for shoring, for instance, are relatively simple to build and have so far been used as temporary shoring walls in constructing underground installations or secondary protective barriers in industrial waste disposal facilities, among others.
However, for efficiently building continuous water blocking walls of sheet piles, gaps of about several millimeters to about 1 to 2 cm are inevitably formed in joint sections of sheet piles, so that water or some other liquid may disadvantageously leak out through those joint sections of sheet pile.
Accordingly, several technologies have so far been proposed for the purpose of making the joint sections of sheet piles water-cutoff (water blocking), as follows.
For example, a coating composition is proposed in Japanese Kokai Publication Sho-59-166567 and Japanese Kokoku Publication Hei-04-25990 which comprises utilizing an NCO-terminated urethane prepolymer prepared by reacting a polyether polyol with an organic diisocyanate. However, the coating film formed can itself absorb water and shows a low degree of swelling (in order that adhesion on swelling and water absorption may be reconciled) and, therefore, is disadvantageous in that, for filling relatively wide gaps (about 5 to 10 mm), it is necessary to apply the composition thickly and, as a result, the coating films may readily peel off at the time of driving the sheet piles into the ground and the water blocking performance cannot be fully obtained in many instances.
In addition, since the main component is a polyether polyol, the composition is insufficient in chemical stability and may readily be degraded during water blocking (in particular of a chemical substance or a like liquid other than water), hence has a problem from the long-term physical properties viewpoint.
Japanese Kokoku Publication Hei-06-96688 proposes a water-swellable (water-absorbing and swelling) coating composition comprising a solution of an electrolytically dissociable water-absorbing polymer, a polyvalent metal compound and an elastomer in an organic solvent. However, since the water-absorbing polymer is further crosslinked with the polyvalent metal compound and the binder used therein is an elastomer having low (or no) hydrophilicity, the composition is low in swelling capacity and, therefore, for filling a relatively wide gap (about 5 to 10 mm), thick coating therewith is required. As a result, there is a drawback that the coating films may readily peel off at the time of driving the sheet piles into the ground and the water blocking performance cannot be fully obtained in many cases. Furthermore, when the composition is used in a temporary water blocking wall or the like, the elastomer used as binder can hardly be stripped off from the sheet piles. There is a further drawback of the composition that it is very difficult to remove the composition from the sheet piles recovered by extraction.
Japanese Kokai Publication Hei-02-206620 proposes a strip-shaped water-swellable substance which comprises a film formed by applying a solution of a highly water-absorbing polymer and a thermoplastic elastomer in an organic solvent to a release paper, followed by drying, and which is to be adhered to the joint section of a sheet pile. There is a drawback, however, that this substance is much inferior in the efficiency (workability) of application to those joint sections of sheet piles or the like which are complicated in shape as compared with coating application by spraying, for instance.
Japanese Kokai Publication Hei-01-252669 discloses a water-absorbing material which comprises a mixture, molded in a desired shape, of a finely divided water-absorbing resin with a water absorbency of 2 to 50 times and a particle size of not more than 100 xcexcm and a thermoplastic resin or elastomer. However, when such a water-absorbing materials is used, the swelling of the water-absorbing resin within the coating film is inhibited due to the hydrophobicity of the thermoplastic resin or elastomer; thus, the water blocking performance, namely the capacity of the water-absorbing resin to swell as a result of sufficient absorption of water in the ground to thereby fill up the joint sections of sheet piles and cutoff water (water blocking), decreases.
Japanese Kokai Publication Sho-57-212269 discloses a swelling coating composition which comprises a mixture of a highly water-absorbing polymer as a main component and a solution, in an organic solvent, of a water-insoluble, film-forming polymer showing a water absorbency of not less than 0.5. Since, in such a swelling coating composition, the water-insoluble, film-forming polymer having a water absorbency of not less than 0.5 is not designed to have an adequate degree of hydrophilicity, there is room for contrivance to for retaining the binder function thereof in the step of absorption of water in the ground without inhibiting the swelling of the water-absorbing resin.
As discussed hereinabove, there has never been a water blocking agent in the art that is (1) readily applicable to the substrates (joint sections of sheet piles), (2) less peelable from the substrates (joint sections of sheet piles) in the step of driving them into the ground, (3) high in swelling capacity (for thin films to be high in water blocking performance) and (4) readily removable from the substrates (e.g. joint sections of sheet piles) after use.
In view of the above-mentioned state of the art, it is an object of the present invention to provide a coating for water blocking agents which is {circle around (1)} easy to apply to the substrate (e.g. joint sections of sheet pile), in particular {circle around (2)} less peelable from the substrates (joint sections of sheet pile) in the step of driving them into the ground, {circle around (3)} high in swelling capacity (for even thin films to be high in water blocking performance) and {circle around (4)} readily removable from the substrate (e.g. joint sections of sheet pile) after use.
Another object of the invention is to provide a sheet pile or steel tubular pipe for water blocking construction methods to which the above coating for water blocking agents has been applied in advance to form a water blocking coating film less peelable in the step of driving the sheet pile into the ground and showing high water blocking performance, and a water blocking construction method which comprises utilizing the above coating for water blocking agents and/or the sheet pile or steel tubular pipe for water blocking construction methods and which is good in workability (with less peeling on the occasion of driving the sheet pile into the ground) and high in water blocking performance and enables easy recovery and cleaning of the sheet pile after use.
The present inventors studied intensively in an attempt to solve the above problems and in search for a coating for water blocking agents which is {circle around (1)} easy to apply to the substrate (e.g. joint sections of sheet pile), {circle around (2)} less peelable from the substrates (joint sections of sheet pile) in the step of driving them into the ground, {circle around (3)} high in swelling capacity (for even thin films to be high in water blocking performance) and {circle around (4)} readily removable from the substrate (e.g. joint sections of sheet pile) after use.
As a result, they found that the above problems can be solved by applying, to the substrate in advance, a coating for water blocking agents which comprises a water-absorbing resin (a), a hydrophilic binder resin (b) and a solvent (c) as essential components and in which the hydrophilic binder resin (b) has an acid value within a specific range. They also found that the effects of the invention can be more fully produced when the above coating for water blocking agents forms a water blocking coating film on the steel material surface and when the ratio (X/Y) between the adhesion (X) of the water blocking coating film to the steel material surface and the breaking strength (Y) of the above water blocking coating film is not less than 0.5. They further found that a water blocking construction method which comprises utilizing a sheet pile or steel tubular pipe for water blocking construction methods to which the above coating for water blocking agents has been applied in advance, or which comprises utilizing the above coating for water blocking agents and the sheet pile or steel tubular pipe for water blocking construction methods can improve the efficiency of a foundation work or the like in the field of civil engineering and construction. Based on these findings, they have now completed the present invention.
Thus, the invention provides a coating for water blocking agents
comprising a water-absorbing resin (a), a hydrophilic binder resin (b) and a solvent (c) as essential components
where in said hydrophilic binder resin (b) has an acid value of 40 mg KOH/g to 500 mg KOH/g.
The invention also provides a sheet pile or steel tubular pipe for water blocking construction methods
wherein the above coating for water blocking agents has been applied thereto in advance.
The invention further provides a water blocking construction method
which comprises utilizing the above coating for water blocking agents and/or the above sheet pile or steel tubular pipe for water blocking construction methods.